Preparation of scale salts



March 10, 1942. H. v. FARR ET AL PREPARATION OF SCALE SALTS Filed June 12, 1940 2 Sheets-Sheet 1 i ll 7 a/ I H l/F' w March 10, 1942. H. v. FARR ET AL 2,276,172

PREPARATION OF SCALE SALTS Filed June 12, 1940 2 Sheets-Sheet 2 Patented Mar. 10, 1942 2,276,172 PREPARATION OF S CKLE SALTS Henry V. Farr, Ferguson, and John R. Ruhoff,

Normandy, Mo.,

assignors to Mallinckrodt Chemical'Works, St. Louis, Mo., a corporation of Missouri Application June 12, 1940, Serial No. 340,132

9 Claims.

This invention relates to the preparation of scale salts, and with'regard to certain more specific features, to a method and apparatus for carrying out production automatically and on a commercial scale.

Among the several objects of the invention may be noted the provision of a continuous means for hardening a film of solution, and removing it from its supporting surface in scale form; the provision of means of the class described in which deleterious powdering of dry film is prevented; and the provision of simple apparatus for carrying out the end in view. Other objects will be in part obvious and in part pointed out hereinafter.

The invention accordingly comprises the steps and sequence of steps, elements and combina-- tions of elements, features of construction, and arrangements of parts which will be exemplified in the structures hereinafter described, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings, in which is illustrated one of various possible embodiments of the invention:

Fig. 1 is an end elevation of a machine for carrying out the process;

Fig. 2 is a fragmentary cross section of the machine;

Fig. 3 is a view taken from the left of Fig. 1- with certain wiper elements removed; and,

- Fig. 4 is a diagrammatic view illustrating the invention broadly.

Similar reference characters indicate corresponding parts throughout the several views of the drawings.

Many substances are known which do not give a crystalline product when their solutions are evaporated or solidified, but yield instead a solid, non-crystalline mass. This is particularly typical of natural substances of a gelatinous riature such as glue, gelatin, shellac, and gumsZbut is also encountered in simpler compounds. Among the more important of these latter substances, from a commercial standpoint, are the brown and green forms of ferric ammonium citrate, ferric citrate, ferric ammonium tartrate, iron and quinine citrate, soluble ferric phosphate, ferric potassium tartrate, iron and strychnine citrate, and soluble ferric pyrophcsphate. These compounds are advantageously produced in the form of scales or flakes and are commonly termed scale salts. The scales are irregular fragments perhaps 1 to 4 mm. in maximum plane dimension and usually very thin.

slow, the yield per unit area of drying surface is small, and the removal of the dry salt from the drying surface is a slow, manual operation.

We have found that application of the ordinary principle of continuous drying or congealing of a film of solution, as on a revolving, heated drum, under a wide variety of conditions, does not produce these salts in the desired scale form.

For a few revolutions of the drum a satisfactory product may be obtained, but after a short time the hardened film adheres or bonds so tenaciously to the drum surface that removal by the usual doctor knife causes complete shattering of the dry film and a powder results.

Our studies of this phenomenon have shown that it is relatively independent of the surface condition of the metal, occurring almost as readily and just as inevitably on a drum with a highly polished surface as on one with an ordinary, unpolished surface. These studies have further indicated that the phenomenon is relatively independent of the materials of construction which are useful in the drum drier fabrication.

We have discovered, however, that by a suitable arrangement and sequence of steps, scale salts can be sati factorily produced on drum driers. Briefly, this is done by arranging the point of application of the liquid film, and speed of drum rotation so that enough congealing is effected during a partial rotation to cause selfflaking or scaling of the dried film from a clean surface of the drum. This flaking or scaling is accomplished at a point in the path of movement ahead of that at which the scraper (doctor knife) or the like is located. This avoids the powdering effect of the doctor knife during the scaling operation. Then, the doctor knife is used subsequently, if at all, simply to remove minor particles from the .drum surface which incidentally remain. Thereafter at a subsequent point on the drum, the drum surface is thoroughly cleaned and made free of any remaining scale salt substance. Cleaning and conditioning is done with substances which allow the liquid film to flow smoothly on to the drum, but, we believe, produce a very thin bond-preventing film on drying. Suitable substances, then, act

' substance.

as wetting agents permitting the formation of a uniform liquid film and as bond-preventing fact that the drum in' returning to the point of application of the scale salt solution carried with it particles of hardened scale salt which formed nuclei for strongly anchoring the subsequent coating. which thereupon failed of self removal and even'of satisfactory removal by means of a scraper. Such action, continued, grew progressively worse.

The above-mentioned thorough cleaning of the drum surface may be accomplished at a point on the drum preceding the application of a fresh solution of scale salts by manual washing with a water solution containing the bond-preventing Indefinitely continuous operation is not feasible with distilled water alone.

One of the'objects of the present invention is to obtain indefinitely continuous operation, and for this purpose it is desired to have a scheme for continuously and effectively treating the drum surface between the scaling point and the point of application. To this end, a soap solution (or its equivalent) is used in connection with a mechanical wiper, and it is then found that the scaling is continuous indefinitely. Solutions of detergent compositions composed of sodium alkyl sulphates, including sodium lauryl sulphate, are also satisfactory and produce the desired continuous scaling. A detergent composition of this nature is known on the market as Dreft." We believe that this unexpected resuit is caused by combination of two effects: (1)

the cleansing of the drum, and (2) the modification of its surface characteristics in such a way as to prevent the adhesion of the dry scale i salts. This may involve the formation of a molecular layer of soap on the metal, or modification in some other way, of the forces of affinity which otherwise produce adhesion of the dried salt to the drum surface.

Referring now to the drawings, numeral I indicates a frame which, by means of suitable bearings 3, provides a support for the hollow rotary trunnions 5 of a rotary metal drum drier I.

Pipes 9 pass through the journals 5, and into and out of the drum 1 for heating purposes. For example, one may introduce steam, and the other withdraw condensate. Similar pipes may be applied for cooling purposes, where cooling can be used to effect solidification preparatory to scaling. In the present example, these pipes may be considered as heating pipes for the drum.

The drum 1, for example, may be a known metal drier drum which has a smooth cylindric surface. It is rotated at a suitable speed by a driving train, not shown because any of various types are useful for the purpose. I

At numeral II is shown a weir box in which is maintained a predetermined level of the liquid 3 to be applied to the drum 7. Suitable supply and overfiow pipes l5 and I1 respectively accomplish this end in the known way.

At 9 is indicated 'a receiver for flaked or scaled material.

Numeral 2| indicates a scraper or so-called doctor knife, the purpose of which herein is, not

to effect the primary removal of material for production purposes, but simply to effect removal of any nuclear particles of material which do not self-flake or scale.

Cleaning of the drum surface, beyond the point of removal of material therefrom is effected automatically by providing a wiper cloth 23 (Fig. 2) which is provided with -a suitable canvas or like backing 25 stretched over supports 21. Fastening means 29 are provided in conjunction-with draw hooks 3|. The latter also hook over a bar 33 to provide for pulling the cloth 23 taut over the supports 21 and by tension against the drum I. Suitable turnbuckles 35 provide for adjusting tension.

At numeral 31 is shown a supply pipe for treating-fiuid such as soap water which is sprayed upon the wiper 23 and trickles down. Excess fiuid which tends to advance down around the drum below the wiper is deflected by spring defiectors 39 and drops down into a receiver 4|.

The supporting rods 21 and "are carried in a frame 5| (see Fig. 3 wherein the wiper 23 and its appurtenances have been removed). This frame pivots at 54 (Fig. 1). Splash plates 5! are used between the frame 5| and the ends of the supports 21 and 33.

At numerals 53 are shown rotary arms which,

as shown in Fig. 3, may be swung in behind the frame 5| when the latter is rotated into a position toward the drum. Clamp screws 55 operated by hand crank 56 which are threaded through the ends of the arms 53, may then be rotated to force the wiper assembly into position against the drum. The screws press on pads 58. When it is desired to withdraw the frame 5|, the screws 55 are loosened. Arms 53 are then swung out of the way and the frame 5| may be pivoted back (to the left in Fig. 1).

The scraper 2| is supported upon a rotary shaft 42 which carries a lever 43. Pinned to the lever 4315 a connecting rod 45 which is threaded into ,a swivel nut 41. The nut 41 is pivoted with respect to the frame I on trunnions 48. A hand wheel 49, into which shaft 45 is threaded, serves to adjust the rod 45 and hence the angle of the shaft 4| and the position and tension of the scraper or doctor knife 2| with respect to the cylinder I.

In operation, a concentrated solution of the desired material (salt) is fed from the weir II to the surface of the drum 1, which is heated internally to the desired temperature and slowly rotated. As the film dries it first cracks and becomes somewhat wrinkled -(see numeral 8 in Fig. 4), and as drying continues, it finally completely detaches itself from the drum (see numeral III in Fig. 4) intheform of flakes or scales, which fall into the receptacle l9. Very little of the material reaches the scraper 2| Since the scraper 2| operates on dry material, the surface of the drum at |2 as it leaves the knife is not entirely free of all'particles of the material, few as they may be. The wiper 23 dissolves orremoves these (or both) and provides the proper soap or like film, so that, upon reapplication of material at the weir II, the next revolution of the drum will again effect the function self-scaling described; .Although soap water is an example of a material which will provide the proper surface cleaning .and treatment for success, equivalents may be used.

The following example of operation of test equipment is given in detail for completeness of disclosure: 1

The drier was a cylindrical drum 36 inches in diameter by '72 inches face width having a calculated drying surface of 56 square feet. It was made of polished stainless steel and heated internally by steam. The feed, scraper, and washing arrangement were related as shown in Fig. 4.

With the drum at 185200 F. and rotating at a speed of 0.5 R. P. M., a solution of Ivory soap containing 0.2% soap by weight was dropped at the rate of 20 gallons per hour on to the drum at the wiping pad by means of a spray pipe. This amount was sufficient to keep the pad wet and to wash away any accumulation of material. A solution of brown iron ammonium citrate (1.5 sp. gr. at 25 C.) was then placed in the weir box and allowed to flow on to the drum. By the time the drum reached the scraper most of the salt had popped off in the form of the desired scales and continued to do so without interruption for continuous runs of several days duration at the rate of 50 lbs. per hour.

Continuous wiping of the drum with water suitably impregnated with small amounts of bond-preventing substances other than soap may be used. Or, ethyl alcohol aluminum stearate,

zinc stearate, or talc may be used. They permit,

continuous operation for some materials for short continuous runs. We have found in general, however, that wiping with a dilute soap or other detergent solution gives the indefinitely continuous performance desired.

It will be understood that, although the scraper 2| provides a powder which may drop into the product box IS, the amount of this is so small that it is immaterial that it appears in the prodnot. If desired, this powdery material may be treated as waste or returned to solution by delivering it to a separate box for re-application.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As many changes could be made in the construction and method without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

We claim:

1. The process of manufacturing scale salts in scale form, comprising continuously and cyclically moving a heated surface with respect to a point of application, applying a liquid film of a solution of the salt to said surface at the point of application for hardening and self-scaling at a subsequent point, and cleaning said surface during its cyclic movement at a region between the scaling point and the application point and applying a film of a bond-preventing material thereto.

2. The process of manufacturing scale salts in scale form, comprising continuously and cyclically moving a heated surface with respect to a point of application, applying a liquid film 'of a solution of the salt to said surface at the point of application for hardening and self-scaling at a subsequent point, and cleaning said surface in its cyclic movement at a region between the scaling point and the application point with a cleaning 3. The process of manufacturing scale salts in scale form, comprising continuously and cyclically moving a fixed surface with respect to a point of application, applying a liquid film of a solution of the salt to said surface at the point of application for hardening and self-scaling at a subsequent point, scraping the surface between said scaling point and the application point and continuously cleaning and applying a bond preventing film to said surface between the scraping point and the application point. 7 e

4. The method of producing scale salts comprising continuously rotating a heated surface from and to a point of application of liquid thereto, applying a liquid solution of the salt to said surface at said point, in a film, for drying and self-scaling at a second point, and treating said surface in its rotary movement from the second point to the first point with a solution for cleaning and conditioning of the surface to insure self-scaling at said second point continuously for indefinite periods.

5. The method of producing scale salts comprising continuously rotating a metal surface from and to a point of application of liquid thereto, heating the surface, applying a liquid solution of the salt to said surface at a point in 6. The process of manufacturing a scale salt I comprising rotating 9. cylindric .surface from and to a first point, heating said surface, applying a film of a liquid solution of the salt to the surface at said point, said salt under the heated conditions drying and self-scaling from the surface at a second point, and continuously treating said surface between the second and first points with a bond-preventing material for cleaning and conditioning the surface so that said scale salt is continuously self-scaling at said second point.

7. The method of treating a non-crystalline scale salt which comprises applying a film of a solution of the salt to a drum drier for hardeningand self-scaling at a subseqeunt point, heating the drum drier. and cleaning and applying a film of a bond-preventing substance to the drum before applying the salt and after the scaling point. 1 '8; The method of treating a non-crystalline scale salt which comprises applying a film of a solution of the salt to a drum drier for hardening and self-scaling at a subsequent point, heating the drum drier, and cleaning and applying a thin film of a bond-preventing substance to the drum before applying the salt and after the sealing point.

9. The method of treating a non-crystalline scale salt which comprises applying a film of a solution of the salt to a drum drier for hardening and self-scaling at a subsequent point, heating the drum drier, and cleaning and applying a substantially molecular film of a bond-preventing substance to the drum before applying the salt and after the scaling point.

HENRY v. FARR. JOHN R. RUHOFF. 

